Build #1: Undetectable stair trap
I came up with this a while ago. It sits an item right underneath the edge of a stair block, which will get picked up unless their inventory is full. The only way somebody would detect it is if they heard the dispenser firing out another item after it decayed, and they got curious and started digging around. I didn't include a killing method for this, since that's really up to you. You could literally do anything- lava, harming potions, pit trap, etc. Use your imagination.
Build #2: Russian Roulette game
Works like Russian Roulette. Place an arrow in the hoppers (chamber) and "spin" it by flipping the lever. The arrow will circle around until you hit the lever again, and presumably will stop somewhere unknown. The two players take turns by hitting the button until somebody gets shot. The arrow gets transported to the next hopper after each firing, simulating a revolver.
Build #3: Dice roller
This uses 6 binary number generators hooked up to lamps to generate a random 1-6 combination. Nothing much else to say about it. Maybe you could re-create Yahtzee in minecraft or some kind of giant Monopoly game.
Build #4: Ridiculously long timer
I'm not sure what this could be used for, but it's a ridiculously long timer. I don't actually have this in my base, but I thought it was neat anyway. It can be configured to power, maximum, roughly every 264 days in vanilla minecraft (real days, not minecraft days) and then reset itself. Might be kind of useless as a measure of time, since it would only be accurate if it was located in the spawn chunks loaded 24/7. But maybe you could think of a way to use it. Maybe you want something to happen once every few hours, days, weeks, months or whatever. You can configure the torches to shorten the timer. So for example if you wanted a 32 hour timer you'd make sure the signal power going into the sides of the comparators equal to 1, so that they would reset every 23 items. You could do that with torches, items in a chest with a comparator, or whatever you want.
I didn't work very hard to make this compact or user-friendly, but if anybody really wants to implement this somewhere I can help you out with the way it works.
